Research News

UB researchers build ultimate solar-powered water purifier

Researchers used this floating solar still prototype for some of the experiments. The device, which they call a “solar vapor generator,” cleans or desalinates water by using the heat converted from sunlight. Image: University at Buffalo.

By CORY NEALON

“The solar still we are developing would be ideal for small communities, allowing people to generate their own drinking water much like they generate their own power via solar panels on their house roof.”

Zhejun Liu, UB visiting scholar

You’ve seen Bear Grylls turn foul water into drinking
water with little more than sunlight and plastic.

Now, academics have added a third element — carbon-dipped
paper — that may turn this survival tactic into a highly
efficient and inexpensive way to turn saltwater and contaminated
water into potable water for personal use.

The idea, which could help address global drinking water
shortages, especially in developing areas and regions affected by
natural disasters, is described in a study
published online Jan. 30 in the journal Global Challenges.

“Using extremely low-cost materials, we have been able to
create a system that makes near maximum use of the solar energy
during evaporation. At the same time, we are minimizing the amount
of heat loss during this process,” says lead researcher
Qiaoqiang Gan, associate professor of electrical engineering in the
School of Engineering and Applied Sciences.

Additional members of the research team are from UB’s
Department of Chemistry, Fudan University in China, the University
of Wisconsin-Madison and the lab of Gan, who is a member of
UB’s New York State Center of Excellence in Materials
Informatics and UB’s RENEW Institute, an interdisciplinary
institute dedicated to solving complex environmental problems.

Solar vapor generator

To conduct the research, the team built a small-scale solar
still. The device, which they call a “solar vapor
generator,” cleans or desalinates water by using the heat
converted from sunlight. Here’s how it works: The sun
evaporates the water. During this process, salt, bacteria or other
unwanted elements are left behind as the liquid moves into a
gaseous state. The water vapor then cools and returns to a liquid
state, where it is collected in a separate container without the
salt or contaminants.

“People lacking adequate drinking water have employed
solar stills for years; however, these devices are
inefficient,” says Haomin Song, a UB PhD candidate and one of
the study’s leading co-authors. “For example, many
devices lose valuable heat energy due to heating the bulk liquid
during the evaporation process. Meanwhile, systems that require
optical concentrators, such as mirrors and lenses, to concentrate
the sunlight are costly.”

The UB-led research team addressed these issues by creating a
solar still about the size of a mini-refrigerator. It’s made
of expanded polystyrene foam (a common plastic that acts as a
thermal insulator and, if needed, a flotation device) and porous
paper coated in carbon black. Like a napkin, the paper absorbs
water, while the carbon black absorbs sunlight and transforms the
solar energy into heat used during evaporation.

The solar still converts water to vapor very efficiently. For
example, only 12 percent of the available energy was lost during
the evaporation process, a rate the research team believes is
unprecedented. The accomplishment is made possible, in part,
because the device converts only surface water, which evaporated at
44 degrees Celsius.

Efficient and inexpensive

Based upon test results, researchers believe the still is
capable of producing 3 to 10 liters of water per day, which is an
improvement over most commercial solar stills of similar size that
produce 1 to 5 liters per day.

Materials for the new solar still cost roughly $1.60 per square
meter — a number that could decline if the materials were
purchased in bulk. (By contrast, systems that use optical
concentrators can retail for more than $200 per square meter.) If
commercialized, the device’s retail price could ultimately
reduce a huge projected funding gap — $26 trillion worldwide
between 2010 and 2030, according to the World Economic Forum
— needed for water infrastructure upgrades.

“The solar still we are developing would be ideal for
small communities, allowing people to generate their own drinking
water much like they generate their own power via solar panels on
their house roof,” says Zhejun Liu, a visiting scholar at UB,
PhD candidate at Fudan University and one the study’s
co-authors.

The research was funded, in part, by the U.S. National Science
Foundation, the National Science Foundation of China and the
Chinese Scholarship Council.